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In this paper, we present the development and characterization of a fully differential SiGe BiCMOS low noise amplifier (LNA) with active impedance matching for the readout of superconducting, quantum interference devices (SQUIDs). Impedance matching is particularly important when using the LNA over a broad frequency range and it is achieved using the Miller effect by adding a negative feedback loop. This approach avoids the degradation of the noise performance that is generated by simply using a parallel resistor at the LNA input. Furthermore, this impedance matching implementation preserves the signal to noise ratio (SNR) because both the signal and the noise are divided by 2 due to the negative feedback loop. This was verified by measuring a lower input voltage noise with the LNA input loaded with a 100  Ω resistor at 77 K compared to a short-circuit. In addition, we present simulations and measurements of the LNA frequency response, input impedance and input voltage noise. The obtained performances for the LNA show a flat gain of 173 V/V with a cut-off frequency of 26MHz and a referred input voltage white noise spectral density level of 0.34 nV/ Hz with a corner frequency of 72 Hz in input matching condition. These values are in good agreement with the simulations. Finally, a discussion about the impact of the impedance matching on the SQUID biasing is also presented.

We present the instrument simulator xifusim developed for the X-ray Integral Field Unit X-IFU aboard the planned Athena mission. xifusim aims to be an accurate representation of the entire instrument, starting from a full simulation of the Transition-Edge Sensor (TES) array receiving impact photons unconstrained by the small signal limit. Its output current is then propagated through the entire readout chain, including multiplexing, amplification and the digital readout. The final output consists of triggered records, which can be post-processed to reconstruct the photon energies. The readout chain itself is separated into individual, modular blocks with several possible models for each, allowing the simulation of different readout schemes or models of varying physical accuracy at the expense of run time. New models are implemented as necessary to enable studies of the overall readout chain. Such studies are also facilitated by fine-grained control of the simulation output, including the internal state of intermediate simulation blocks. In addition to its modularity, xifusim also allows the manipulation of certain internal parameters during a run, enabling the simulation of readout chain characterization measurements, environmental drifts or various kinds of crosstalk.

This paper updates the development of a warm front-end electronics (WFEE) dedicated to cryogenic sensors readout. It belongs to the X-ray integral field unit instrument of ESA’s future space observatory: ATHENA. This instrument integrates cryogenic elements such as 3168 transition edge sensors as detectors, multiplexed into 96 channels using time-division multiplexing (TDM). One TDM channel will be read out by two stages of superconducting quantum interference device (SQUID), followed by a WFEE and finally, a digital readout system, both two last stages operating at about 300 K. In the WFEE, 96 TDM channels will be distributed in 48 application-specific integrated circuits (ASIC). Each channel includes one low-noise amplifier to amplify the multiplexed signal and 5 configurable current sources to bias the SQUIDs and TES in the cryogenic stages. Additionally, two channels within the same ASIC share a serial bus “RS485/I 2 C” to configure the current sources (current SlowDACs) and housekeeping elements that monitor the temperature, current and voltage of the ASIC. The ASIC presented in this paper, “AwaXe_v3” (AwaXe: Athena Warm Asic for the X-ifu Electronics), is developed for the WFEE using an AMS 350 nm SiGe BiCMOS technology. It is the first prototype of the WFEE integrating two complete TDM channels. Representative measurement results that characterise the main components of the WFEE will be discussed in this paper as an update on the use of ASIC for the TES/SQUID readout.

CNES (French Space Agency) is in charge of the development of the X-ray Integral Field Unit (X-IFU) instrument for Athena, the high resolution X-ray spectrometer of the ESA Athena X-ray Observatory. X-IFU will deliver spectra from 0.2 to 12 keV with a spectral resolution in the range of 2.5 eV up to 7 keV on a 5′′ pixels, with a field of view > 4′ equivalent diameter. The main sensor array detection chain is a key part of the instrument, being by far the main contributor to its performance. It involves major partners: NASA GFSC, NIST, SRON, VTT, APC, and IRAP. The cryo-harness interconnecting the Focal Plane Assembly cold interface to the Warm Front End Electronics is under CNES responsibility. The different technical solutions are the loom technology and the shielded twisted pair technology. Characterizations have been performed on breadboards to assess the crosstalk performances for each solution. The results of these analysis are a driver to perform the trade-off between the available cryo-harness technologies.

Cosmic microwave background (CMB) spectral science is experiencing a renewed interest after the impressive result of COBE–FIRAS in the early Nineties. In 2011, the PIXIE proposal contributed to reopen the prospect of measuring deviations from a perfect 2.725 K planckian spectrum. Both COBE–FIRAS and PIXIE are differential Fourier transform spectrometers (FTSes) capable to operate in the null condition across ∼ 2 frequency decades (in the case of PIXIE, the frequency span is 30 GHz–6 THz). We discuss a complementary strategy to observe CMB spectral distortions at frequencies lower than 250 GHz, down to the Rayleigh–Jeans tail of the spectrum. The throughput advantage that makes the FTS capable of achieving exquisite sensitivity via multimode operation becomes limited at lower frequencies. We demonstrate that an array of 100 cryogenic planar filter-bank spectrometers coupled to single mode antennas, on a purely statistical ground, can perform better than an FTS between tens of GHz and 200 GHz (a relevant frequency window for cosmology) in the hypothesis that (1) both instruments have the same frequency resolution and (2) both instruments are operated at the photon noise limit (with the FTS frequency band extending from ∼ tens of GHz up to 1 THz). We discuss possible limitations of these hypotheses, and the constraints that have to be fulfilled (mainly in terms of efficiency) in order to operate a cryogenic filter-bank spectrometer close to its ultimate sensitivity limit.

SiGe integrated circuits dedicated to the readout of superconducting bolometer arrays for astrophysics have been developed since more than 10 years at APC. Whether for Cosmic Microwave Background (CMB) observations with the QUBIC ground-based experiment (Aumont et al. in astro-ph.IM, 2016 . arXiv:1609.04372 ) or for the Hot and Energetic Universe science theme with the X-IFU instrument on-board of the ATHENA space mission (Barret et al. in SPIE 9905, space telescopes & instrumentation 2016: UV to γ Ray, 2016 . https://doi.org/10.1117/12.2232432 ), several kinds of Transition Edge Sensor (TES) (Irwin and Hilton, in ENSS (ed) Cryogenic particle detection, Springer, Berlin, 2005 ) arrays have been investigated. To readout such superconducting detector arrays, we use time or frequency domain multiplexers (TDM, FDM) (Prêle in JINST 10:C08015, 2016 . https://doi.org/10.1088/1748-0221/10/08/C08015 ) with Superconducting QUantum Interference Devices (SQUID). In addition to the SQUID devices, low-noise biasing and amplification are needed. These last functions can be obtained by using BiCMOS SiGe technology in an Application Specific Integrated Circuit (ASIC). ASIC technology allows integration of highly optimised circuits specifically designed for a unique application. Moreover, we could reach very low-noise and wide band amplification using SiGe bipolar transistor either at room or cryogenic temperatures (Cressler in J Phys IV 04(C6):C6-101, 1994 . https://doi.org/10.1051/jp4:1994616 ). This paper discusses the use of SiGe integrated circuits for SQUID/TES readout and gives an update of the last developments dedicated to the QUBIC telescope and to the X-IFU instrument. Both ASIC called SQmux 128 and AwaXe are described showing the interest of such SiGe technology for SQUID multiplexer controls.

The X-ray Integral Field Unit(X-IFU) of the Athena observatory, scheduled for launch in the mid2030's, will provide X-ray spectroscopy data with unprecedented spectral and spatial resolution. This will be achieved with a 2kilo-pixel array of transition-edge sensor (TES) microcalorimeters. The complete detection chain is under development by a large international collaboration. In order to perform an end-to-end demonstration of the X-IFU readout chain, a 50 mK test bench is being developed at IRAP in collaboration with CNES. The test bench uses a two-stage ADR cryostat from Entropy GmbH, a 1024-pixelarray, and will initially be operated using a warm electronics chain from NIST and NASA Goddard Space Flight Center. We describe the complete system being installed in the cryostat and the current results obtained with these electronics. We also review the status of the integration of the digital readout electronics (DRE)prototype into the demonstration chain and the plan for integrating and testing the complete X-IFU readout chain.

Superconducting QUantum Interference Device (SQUID) multiplexing is a common technique in the use of large arrays of Transition Edge Sensors (TES). A Time Domain Multiplexer (TDM) combines input TES signals into one output signal using several SQUIDs. Different TES, SQUID and amplifier characteristics induce unavoidable different offsets on the multiplexed signal. Additionally, given the periodicity of the SQUID characteristic, the Flux Locked Loop (FLL) operating point is only defined modulo  Φ 0 . This can lead to a large output offset. In multiplexed mode, the difference between offsets associated with different pixels can induce a parasitic signal which is often larger than that of the TES. These offset signals drastically constrain the readout dynamic range and thus the maximum gain allowed. They also limit the signal-to-noise ratio, the FLL stability and the multiplexing frequency. Offsets in SQUID readout are discussed and offset compensation for TDM is presented. The dynamic calibration and compensation on a simplified 4:1 TDM are demonstrated in simulation. Dynamic offset compensation is being implemented on a cryogenic SiGe integrated circuit operated at 4 K for 128:1 TDM.

Thermometer circuit can be designed in BiCMOS technology to measure directly the on-chip temperature right close to other functions of an Application Specific Integrated Circuit (ASIC). This paper discusses on-chip thermometry with high temperature sensitivity. The setting of an operating point around 50 °C with no-offset is discussed allowing a multiplication of the output current times ten for a better sensitivity. An analytical model based on a proportional to temperature cell and a complementary to absolute temperature cell is discussed. Linear response in the [-150 °C: +150 °C] is illustrated. However, out from this range, deviations between analytical models and simulations based on foundry models are discussed pointing the importance of the setting point depending on the temperature range.